Method of forming a thin film magnetic structure having ferromagnetic and antiferromagnetic layers

ABSTRACT

A method of forming a magnetic structure having layers with different magnetization orientations provided by a common magnetic bias layer includes the steps of depositing an antiferromagnetic layer between first and second ferromagnetic layers. During the deposition of the first and second ferromagnetic layers, magnetization fields of different orientations are employed separately to induce different directions of magnetization in the first and second layers. The different directions of magnetization in the first and second layers are sustained, through the process of exchange coupling, by the interposed antiferromagnetic layer which serves as the bias layer. A magnetic structure thus fabricated, can be used as a read transducer capable of generating differential signals with common mode noise rejection, and can be used as a magnetic pole for a magnetic head with reduced Barkhausen noise.

FIELD OF THE INVENTION

This invention relates to the formation of thin film magnetic assembliesand in particular to a method of forming thin films for magnetic headsor sensors with ferromagnetic (FM) and antiferromagnetic (AFM) layers.

BACKGROUND OF THE INVENTION

Presently known magnetic heads or transducers incorporatemagnetoresistive (MR) sensors for detecting magnetically recorded data.A magnetoresistive transducer can read information on a recording mediumwith much narrower track widths and yields better signal-to-noise ratio.Also, the output signal generated during the data reading process isindependent of the traveling speed of the recording medium.

A typical magnetoresistive head includes a magnetoresistive sensorlocated between two magnetic shield layers. Disposed between themagnetoresistive sensor and the magnetic shield layers are insulatinglayers. During the data reading mode, the magnetic shields shunt awaystray fields, thereby confining the magnetic flux that emanates from arecord medium and which is sensed by the MR sensor. The changes inmagnetic flux correspondingly vary the resistivity of themagnetoresistive sensor. A direct electric current passing through themagnetoresistive sensor generates a varying voltage which represents thedata stored in the recording medium.

Implementations of MR read heads at a miniaturized scale encountervarious practical problems. First, the MR sensor needs to be properlybiased. The ferromagnetic layer in its natural state comprises amultiple number of magnetic domains separated by domain walls. Thesedomain walls are highly unstable. During normal operations, the constantmerging and splitting of the domain walls generate undesirable signalnoise, commonly called Barkhausen noise, which degrades the performanceof the magnetic head. To suppress the signal noise, hard magnetic biaslayers are normally attached to the ferromagnetic layers for the purposeof aligning the magnetic domains in a single domain configuration.Furthermore, to position the ferromagnetic layer in the linear operationregion, another bias, called transverse bias, needs to be provided tothe ferromagnetic layer. A soft adjacent layer formed of a material withrelatively high coercivity and minimal magnetoresistive response isdisposed adjacent to and spaced from the ferromagnetic layer to providethe necessary transverse bias. Exchange coupling betweenantiferromagnetic (AFM) and ferromagnetic (FM) materials is also used toachieve such biases. In more recent recording devices, such as spinvalve heads, the AFM/FM structure becomes the critical part of thedevice. An AFM/FM structure with superior magnetic properties willenhance devices such as spin valve heads, dual MR heads and dual spinvalve heads. Also in inductive devices wherein lamination is used toreduce eddy current and extend high frequency performance, insulatingAFM materials may be used as lamination spacers to strengthen signaldomain structure in the pole pieces of the inductive head. This approachcan significantly reduce signal noise and enhance high frequencyperformance.

For the above reasons, there is a need to provide a method offabricating magnetic transducers and magnetic film structures that caninteract with storage media having narrow recorded data tracks with highlinear recording densities, yet sufficiently sensitive to sense only thedata signals recorded on the magnetic media with undesirable signalnoise screened out.

SUMMARY OF THE INVENTION

An object of the invention is to provide a method of fabricatingmagnetic transducers capable of interacting with storage media havingnarrow data tracks with high linear recording densities.

Another object of the invention is to provide a method of fabricatingmagnetic read transducers with high sensitivity for sensing recordedsignals from magnetic media while screening out undesirable signalnoise.

Another object of the invention is to provide a method of fabricatingmagnetic film structures that can be used in laminated pole pieces freeof Barkhausen noise.

A further object of the invention is to provide a method of fabricatingmagnetic read transducers with simplicity of design and reduction ofprocessing steps thereby realizing lower manufacturing costs.

According to this invention, a thin film magnetic structure isfabricated by depositing an antiferromagnetic layer between first andsecond ferromagnetic layers in a sandwich type structure. During thedeposition of the first and second ferromagnetic layers, magnetic fieldsof different orientations are applied, thereby inducing magnetizationdirections of different orientations in the first and secondferromagnetic layers. The different directions of magnetization in thefirst and second ferromagnetic layers are sustained by the interposedantiferromagnetic layer through exchange coupling. The magneticstructure can be used as a read transducer capable of generatingassertive and complementary signals with common mode noise rejection. Inaccordance with this invention, there is only one layer, theantiferromagnetic layer, which provides magnetic biasing. The interposedantiferromagnetic layer forces single domain states in the first andsecond ferromagnetic layers, thereby eliminating the merging andsplitting of domain walls and minimizing Barkhausen noise. A magneticstructure fabricated from the inventive method can also be used as amagnetic pole for an inductive write transducer.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail with reference to thedrawings in which:

FIGS. 1A, 1B, 1C and 1D are isometric views, partly broken away,illustrating one method of forming a magnetic structure having layerswith antiparallel magnetization orientations provided by a commonmagnetic bias layer;

FIG. 2 is a cross-sectional side view showing the internal constructionof a sputtering apparatus used for material deposition;

FIG. 3A is an exploded view showing the magnetization vectorsrepresenting unidirectional magnetic orientations in the layers of themagnetic structure antiparallel to one another.

FIG. 3B is a hysteresis curve depicting the magnetic characteristics ofthe structure illustrated in FIGS. 1A-1D, with applied characterizationfield 60;

FIG. 4A is an exploded view showing the magnetization vectorsrepresenting unidirectional orientations in the layers of the magneticStructure perpendicular to each other;

FIGS. 4B and 4C are hysteresis curves depicting the magneticcharacteristics of the layers shown in FIG. 4A with FIG. 4B underapplied field 60 and FIG. 4C under applied field 74;

FIG. 5A is an exploded view showing the magnetization vectorsrepresenting unidirectional magnetic orientations in the layers of themagnetic structure 45° apart; and

FIGS. 5B and 5C are hysteresis curves depicting the magneticcharacteristics of the magnetic structure shown in 5A, with FIG. 5Bunder applied field 60 and FIG. 5C under applied field 92.

Like reference numerals refer to like parts.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1A-1D and FIG. 2, a substrate 2 is provided whichcan be a single piece substrate, or a substrate with other predepositedlayers, for example. Alternatively, the substrate 2 can be part ofanother thin film structure. For instance, the substrate 2 can be apartially finished transducer in which the method of the presentinvention is employed to overlay a magnetic shield or pole layer abovethe transducer. Prior to deposition of any subsequent layers, thesurface of the substrate 2 needs first to be polished and cleaned. Thesubstrate 2 is located in a deposition chamber, such as the chamber 4 ofa sputter apparatus 6 as shown in FIG. 2. An example of a sputterapparatus that can be used is model number 4400E, made by Perkin Elmer,Inc., of Mountain View, Calif. The substrate 2 is placed onto asubstrate fixture 8 inside the chamber 4. The chamber 4 is then degassedthrough an gas outlet 10. After a satisfactory vacuum level inside thechamber 4 is reached, an inert gas, such as argon (Ar), is admitted intothe chamber 4 through a gas inlet 12. When the inert gas inside thechamber 4 reaches a sufficiently high pressure level, the sputterer isthen ready for deposition. In case of reactive sputter deposition,another gas such as oxygen is admitted to the chamber.

Inside the chamber 4, there is a target plate 14 which comprises thematerial to be deposited onto the substrate 2. The target plate 14 andthe substrate fixture 8 are normally biased through a very steepelectric potential by the voltage source 16 in the range of 500 Volts to1000 Volts. The inert gas or mixture of inert and reactive gases betweenthe target 14 and the substrate fixture 8 are thereby ionized. Inessence, the electrons are attracted toward the substrate fixture 8while the positively charged ions 18 are striking toward the target 14.In the process, the target molecules 20 are dislodged and dispersed fromthe target 14 and deposit onto the substrate 2 as a deposited layer ofthe target material. In reality, the gas ions 18 form a plasma 24bombarding the target 14 constantly.

Simultaneously with the deposition process, electromagnets 26 inside thechamber 4 are activated, generating magnetic field 26 traversing thesubstrate 2. The purpose of the magnetic field 28 is to induce anuniaxial anisotropy in the first ferromagnetic layer 22 (FIG. 1B). Theresultant structure up to this step is shown in FIG. 1B, in which themagnetic field 28 is also illustrated.

Next in the processing sequence is the step of depositingantiferromagnetic material. During deposition of the antiferromagneticmaterial, the electromagnets 26 are kept on to induce the unidirectionalanisotropy in layer 22. The rest of the deposition process for this stepis substantially the same as described above and is not furtherelaborated for the sake of clarity and conciseness. The resultantstructure after this depositing step is shown in FIG. 1C, in which theantiferromagnetic layer is designated by reference numeral 30.

What follows is the step of depositing a second layer of ferromagneticmaterial 32. The method of depositing this layer 32 is substantiallysimilar to the step of depositing the first layer 22 with the exceptionthat during deposition, the electromagnets 26 are reversely energizedthereby generating a magnetic field 34 with a different magnetizationdirection than the magnetic field 26 (FIG. 2). For the same reason asdiscussed above, the magnetic field 34 is utilized to induce anotherunidirectional anisotropy on the second ferromagnetic layer 32. Theresultant structure up to this step is shown in FIG. 1D in which themagnetic field 34 is also depicted.

Next in the processing sequence is the step of depositingantiferromagnetic material. During deposition of the antiferromagneticmaterial, the electromagnets are kept on to maintain the magneticorientation in the layer for establishing the first pinning directionwith the subsequent antiferromagnetic layer. The rest of the depositionprocess for this step is substantially the same as described above andis not further elaborated for the sake of clarity and conciseness. Theresultant structure following this deposition step is shown in FIG. 1C,in which the antiferromagnetic layer is designated by reference numeral30. After layers 22 and 30 are deposited, an unidirectional anisotropyis established in layer 22 with its direction defined by the polarity ofthe applied magnetic field.

What follows is the step of depositing a second layer of ferromagneticmaterial 32. The method of depositing layer 32 is substantially similarto the step of depositing the first layer 22 with the exception thatduring deposition, the electromagnets 26 are reversely energized therebygenerating a magnetic field with a different magnetization directionthan the magnetic field 28 (FIG. 2). For the same reason as discussedabove, the magnetic field 34 is utilized to induce anotherunidirectional anisotropy on the second ferromagnetic layer 32. Theresultant structure up to this step is shown in FIG. 1D in which themagnetic field 34 is also depicted.

In the preferred method, the thickness of the first and second layers offerromagnetic material 22 and 32 is each deposited within the range of100 Å to 200 °. The antiferromagnetic material layer is deposited to athickness of between 250 Å to 500 Å. The B-H hysteresis loop of thestructure shown in FIG. 1D is illustrated in FIG. 3B, where layers 22and 32 are each exchange coupled in opposite directions. As a result, asplit loop is formed. Layers 22 and 32 possess the same exchangestrength in magnitude but are shifted to opposite field polarity.

In FIGS. 1A, 1B, 1C and 1D applied field 34 is made opposite to field26, that is, a 180° difference. The resultant hysteresis loop for thestructure shown in FIG. 1D is illustrated in FIG. 3B, with the magneticfield sweeping back and forth along the direction of the bidirectionalarrow 60 of FIG. 3A. If the field 34 is applied perpendicular to field26, that is, a 90° difference, the exchange coupling effect and theapplied magnetic field will exchange bias layer 22 along the appliedfield direction 66 and layer 32 along the direction 68, respectively(shown in FIG. 4A). Local exchange anisotropy will 90° apart in thesetwo ferromagnetic layers. When a hysteresis loop is recorded with thefield sweeping along direction 60 as seen in FIG. 4A, layer 22 will berecorded as hard axis characteristics, while layer 32 will appear in anexchange biased state. FIG. 4B reflects this phenomenom. If the field isswept along direction 74 in FIG. 4A, layer 22 will be in an exchangebiased state while layer 32 is in its hard axis state. FIG. 4C showsthis phenomenom. When the applied field 34 is set to be 45° apart fromfield 26 during deposition of layer 32, the resultant local exchangeanisotropy in layers 22 and 32 will be set at 45° apart. FIGS. 5A-5Cdemonstrate the schematics and the recorded loops.

Using only one thin antiferromagnetic film or layer 30 and applying anappropriate magnetic field to ferromagnetic films or layers 22 and 32during deposition, different local exchange anisotropy arrangements canbe established, as pairs 46 and 52, 66 and 68 and 90 and 68.

If the method is used to build a transducer, subsequent steps ofdepositing and patterning can be performed on the resultant structure asshown in FIG. 1D.

While the method of the invention has been described for specificapplications, as illustrated herein, various thin film products can bebuilt utilizing the inventive method. Other variations are possiblewithin the scope of the invention. For example, layers 22, 30 and 32 canbe deposited by methods such as chemical vapor deposition (CVD) orelectroplating. The magnetic fields 28, 34 and 40 can be generated bymeans other than by electromagnets, for example, permanent magnet, andthe change of field orientation canbe achieved by reorienting wafers. Inaddition, the magnetization vectors in the first and second layers 22and 32 can be implemented without a simultaneous magnetic field duringdeposition. Instead, after deposition, the resultant structure can beheated up beyond the blocking temperature and cooled down in a magneticfield, provided that the first and second ferromagnetic layers havedifferent blocking temperatures. Moreover, other materials than thosedisclosed herein can be used to implement the invention.

What is claimed is:
 1. A method of forming a thin film magneticstructure, comprising the steps of:providing a substrate; depositing afirst layer of ferromagnetic material on said substrate in the presenceof a magnetic field oriented in a first direction; depositing a layer ofantiferromagnetic material on said first layer of ferromagneticmaterial; and depositing a second layer of ferromagnetic material onsaidlayer of antiferromagnetic material in the presence of a magneticfield oriented in a second direction, said first layer of ferromagneticmaterial being spaced from said second layer of ferromagnetic materialby said antiferromagnetic material.
 2. The method of forming a thin filmmagnetic structure as set forth in claim 1 wherein said layer ofantiferromagnetic material is electrically insulating.
 3. The method offorming a thin film magnetic structure as set forth in claim 2 whereinsaid layer of electrically insulating antiferromagnetic material isformed of a material selected from the group of NiC--O, Ni--O and Fe₂O₃.
 4. The method of forming a thin film magnetic structure as set forthin claim 1 wherein said first and second magnetic field directions areantiparallel to each other.
 5. The method of forming a thin filmmagnetic structure as set forth in claim 1 wherein said first and secondmagnetic field directions are perpendicular to each other.
 6. The methodof forming a thin film magnetic structure as set forth in claim 1wherein said steps of depositing comprise the step of sputtering or thestep of ion beam deposition.
 7. The method of forming a thin filmmagnetic structure as set forth in claim 1 wherein said first and secondlayers of ferromagnetic material are formed of Permalloy, NiFeCo, FeCoor Co.
 8. The method of forming a thin film magnetic structure as setforth in claim 1 wherein said layer of antiferromagnetic material isformed of ferrous manganese or nickel manganese.
 9. The method offorming a thin film magnetic structure as set forth in claim 1 whereinsaid steps of depositing said layers are performed below the blockingtemperature of said ferromagnetic material.
 10. A method of forming athin film magnetic structure comprising the steps of:providing asubstrate; applying a first magnetic field oriented in a first directionto said structure; depositing a first layer of ferromagnetic material onsaid substrate; depositing a layer of antiferromagnetic material on saidfirst layer of ferromagnetic material; applying a second magnetic fieldoriented in a second direction to said structure; depositing a secondlayer of ferromagnetic material on said layer of antiferromagneticmaterial, such that said first layer of ferromagnetic material is spacedfrom said second layer of ferromagnetic material by said layer ofantiferromagnetic material; and terminating said second magnetic field.11. The method of forming a thin film magnetic structure as set forth inclaim 10 wherein said steps of depositing said ferromagnetic layers areperformed at temperatures below the blocking temperature of saidferromagnetic material.
 12. The method of forming a thin film magneticstructure as set forth in claim 11 wherein said layer ofantiferromagnetic material is formed from a material selected from thegroup comprising NiCo--O, Ni--O, Fe₂ O₃, FeMn and NiMn.
 13. The methodof forming a thin film magnetic structure as set forth in claim 10wherein said first and second directions are antiparallel to each other.14. The method of forming a thin film magnetic structure as set forth inclaim 10 wherein said first and second directions are perpendicular toeach other.
 15. The method of forming a thin film magnetic structure asset forth in claim 10 wherein said antiferromagnetic material comprisesferrous manganeseor nickel manganese.
 16. A method of forming a thinfilm magnetic structure having different magnetization orientationsprovided by a common magnetic bias layer, comprising the stepsof:providing a substrate; depositing a first layer of ferromagneticmaterial on said substrate in the presence of a first magnetic fieldoriented in a first direction, said first magnetic field inducing afirst direction of uniaxial anisotropy in said first layer; depositingon said first layer a layer of antiferromagnetic material having firstand second major surfaces, said first major surface being in contactwith said first layer of ferromagnetic material; and depositing on saidlayer of antiferromagnetic material a second layer of ferromagneticmaterial in the presence of a second magnetic field oriented in a seconddirection, said second layer of ferromagnetic material being in contactwith said second major surface of said antiferromagnetic layer, saidsecond magnetic field inducing a second direction of uniaxial anisotropyin said second layer, said first and second layers of ferromagneticmaterial being spaced from each other by said layer of antiferromagneticmaterial; wherein said first and second directions of uniaxialanisotropy mutually exchange-couple with said first and second majorsurfaces of said layer of antiferromagnetic material, such that saidlayer of antiferromagnetic material constitutes said common magneticbias layer for providing different magnetization orientations as saidfirst and second directions of uniaxial anisotropy in said first andsecond layers of ferromagnetic material.
 17. The method of forming athin film magnetic structure as set forth in claim 16 wherein said firstand second directions are angularly oriented with respect to each other.18. The method of forming a thin film magnetic structure as set forth inclaim 16 wherein said first and second directions are antiparallel toeach other.
 19. The method of forming a thin film magnetic structure asset forth in claim 16 wherein said first and second layers comprisePermalloy and said layer of antiferromagnetic material is formed from amaterial selected from the group comprising NiCo--O, Ni--O, Fe₂ O₃, FeMnand NiMn.
 20. The method of forming a thin film magnetic structure asset forth in claim 19 where said layer of antiferromagnetic material isdeposited to a thickness of between 200 to 250 Angstroms, and each ofsaid first and second layers of ferromagnetic material is deposited to athickness of between 100 to 200 Angstroms.
 21. The method of forming athin film magnetic structure as set forth in claim 16 wherein said stepsof depositing comprise the step of sputtering or the ion beamdeposition.
 22. The method of forming a thin film magnetic structure asset forth in claim 16 wherein said steps of depositing said layers areperformed below the blocking temperature of said ferromagnetic material.23. The method of forming a thin film magnetic structure as set forth inclaim 16, including the step of patterning electrical lead layers incontact with said first and second layers of ferromagnetic material.